Projectors based on a light valve which controls the transmission or not of light therethrough by a scattering effect are known. See, e.g., Fergason, U.S. Pat. No. 4,693,557 (1987) and Jones et al., U.S. Pat. No. 5,075,789 (1991). A characteristic of such projectors is that brightness and contrast are both a function of the projection aperture. As the projection aperture decreases the contrast ratio increases but the brightness decreases, so that an improvement in one parameter is offset by a decrement in the other parameter. The situation is further complicated by the fact that projectors are not necessarily used in wholly darkened rooms, but, rather, under a variety of ambient lighting conditions. For instance, it may be desirable to have some minimal ambient lighting present to permit viewers to take notes of a presentation. So, a contrast ratio-brightness combination which may be optimized for a particular set of ambient lighting conditions may not be suitable for a different set of ambient lighting conditions.